An organic light-emitting diode (OLED) is a diode that realizes display using reversible color changes generated by an organic semiconductor material driven by a current. A basic structure of an OLED display device usually includes a hole transport layer, a light-emitting layer, and an electron transport layer. When a power supply supplies an appropriate voltage, a hole of an anode and electrons of a cathode can be combined together in the light-emitting layer to produce light. Compared with a thin-film field-effect transistor liquid crystal display, the OLED display device is characterized by high visibility and high brightness, more energy-efficient, light-weight, and thin in thickness. Therefore, the OLED display device is regarded as one of the most promising products in the twenty-first Century.
Because the brightness of the OLED is related to the magnitude of the current passing through the OLED, the electrical properties of a thin-film transistor used for driving will directly influence the display effect, and particularly a threshold voltage of the thin-film transistor often drifts to enable the entire OLED display device to generate a problem of uneven brightness.
In order to improve the display effect of the OLED, the threshold voltage of the driving transistor usually needs to be detected in real time, and pixel compensation is then carried out on the OLED through the pixel driving circuit. The existing pixel driving circuit requires a large number of metal wires to detect a threshold voltage of the driving transistor, which results in that the pixel driving circuit occupies a larger space in the OLED display device, and a narrow frame of the OLED display device is difficult to realize.